Polycrystalline silicon Society for Information Display International Symposium Digest of Technical Papers (1999), thin-film transistors (TFTs) are higher in carrier mobility than amorphous TFTs by more than two orders of magnitude, and thus offer excellent performances. Examples utilizing this feature include an active-matrix liquid crystal display (AM-LCD) device as disclosed, for example, in p. 172. This LCD device is arranged so that peripheral drive circuitry is partly configured from poly-silicon TFTs, thereby enabling reduction in number of electrical connection nodes or terminals between a pixel part and the peripheral driver circuit. This enables it to visually display high-precision images.
A prior known method for manufacturing a poly-silicon TFT will be described with reference to FIGS. 2A to 2E below. A silicon oxide film BL is deposited as a buffer layer on a glass substrate SUB to a thickness of about 100 nm. An amorphous silicon layer is then deposited thereon by plasma chemical vapor deposition (CVD) techniques to a thickness of 50 nm. Next, XeCl excimer laser light is irradiated for crystallization of the amorphous Si layer. Then, known photo-etching is applied, thereby obtaining an island-shaped polysilicon layer PSI. Thereafter, a gate insulating film GL is deposited by plasma CVD to a thickness of 100 nm, followed by the formation of a gate electrode GM (see FIG. 2A). Next, with the gate electrode being as a mask, a chosen kind of impurity, e.g., phosphorus (P), is implanted to form a lightly-doped n-type polysilicon layer LDN. Subsequently, with a resist as a mask, a heavily-doped n-type polysilicon layer HDN is formed (FIG. 2B). An interlayer dielectric film INL is formed by plasma CVD to entirely cover the resultant layer structure, followed by the formation of source/drain electrodes SDM through contact holes CNT2 as defined in the interlayer dielectric film (FIG. 2C). Thereafter, a passivating insulator film PL made of silicon nitride with a thickness of 500 nm is formed to cover the entirety. A pixel electrode PXM and source/drain electrode SDM is connected together via a contact hole CNT3 as defined in the passivating insulator film PL (FIG. 2D).